1. Field of the Invention
The present invention relates to a spot welding apparatus improved in pressing an overlapped portion of work mounted on a worktable by an electrode attached to a welding arm vertically movable over the worktable to spot-weld the work by passing current between the electrode and the worktable.
In more detail, the present invention relates to a spot welding which can facilitate the exchanging work of various electrodes according to work and further can support various electrodes of different sizes stably.
2. Description of Related Art
As an example of the conventional spot welding apparatus related to the present invention, there is Japanese Published Examined Patent Application No. 3-56148. In this conventional apparatus, the structure is such that a column is stood on a base provided with a worktable for supporting work; a support cylinder is hung vertically from an end portion of a support beam pivotally supported by the column in the horizontal direction; and a welding arm having an electrode at the end portion thereof is pivotally supported at the lower portion of the support cylinder.
In use of the above-mentioned conventional spot welding apparatus, the worker first brings up the electrode attached to the end portion of the welding arm by gripping a handle attached to the base end portion of the welding arm, and further moves the welding arm by holding the welding arm horizontally. Here, since the welding arm is held in the horizontal direction, the welding arm can be moved only horizontally.
Therefore, there exists such a problem in that when the electrode attached to the fee end portion of the welding arm is heavy, for instance, a laborious work is required to bring up the end portion of the welding arm.
In addition, in the conventional structure, a piston rod of a hydraulic cylinder disposed at the upper portion of the afore-mentioned support cylinder and the base end portion of the welding arm are linked with each other by a wire. Therefore, when this wire is pulled, the end portion of the welding arm is pivoted downward, so that the electrode attached to the end portion thereof can press the work mounted on the worktable. As a result, when the worktable is vibrated by an external force, there exists such a problem that the wire is resonated as a string and thereby the contact pressure between the electrode and the work is unstable, with the result that the spot welding itself becomes unstable.
Further, when the spot welding apparatus is used for many hours, there exists another problem in that the wire tends to be elongated or broken at the worst due to fatigue, thus causing a trouble from the standpoint of maintenance.